The invention relates to a method and apparatus for fabricating a hollow body, preferably from sheet metal, such as, for example, an automobile hood, door or the like, wherein the so-called internal hydroforming (IHF) (high pressure forming) process is applied.
German Offenlegungsschrift 42 32 161 describes a method for fabricating a hollow body starting from a body made from blanks, wherein the hollow body is fabricated by the combined use of the IHF process and the deep drawing process. The distinctive feature of this proposed method is that the initial workpiece is first fabricated from two blanks having identical edge dimensions, which are placed upon one another and welded together at the edges. After placing the initial workpiece in a press die and closing the die, the forming of the starting body to a hollow body takes place by the above-mentioned process. When the forming process is complete, further processing steps follow.
Apart from the fact that in this proposed method an initial workpiece has to be separately fabricated and then placed in the press die-which requires at least two additional process steps-this method suffers from the disadvantage that because of the weld bead only workpieces which are symmetrical in respect of their upper and lower parts can be fabricated. Moreover in the border region of the component the hollow body must be further treated after the forming on account of surface damage by the deep drawing: this is followed by still further processing steps such as, for example, cropping of the wide flanges caused by the type of forming and/or post-spot welding of the connection between the blanks, which must be done in further separate work stations. The method is thus distinguished by requiring numerous processing steps which must be carried out in succession, and is extremely limited in respect of its product range.
Against this background, it is the object of the invention to provide a method of fabricating a hollow body which, having regard to the constantly growing pressure on time and costs, particularly in the automobile industry, is more efficient and thus more economical and is also more adaptable.
In accordance with the invention, this object is achieved by a method of fabricating a hollow body such as, for example, an automobile hood, door or the like, in which at least two blanks, preferably consisting of sheet metal, are held sealingly together along an at least almost completely closed line, the hollow body is shaped by means of the internal hydroforming (IHF) process, and the mutually connected blanks are clinched together.
The method is also particularly suitable for the fabrication of multi-walled components which are specially suitable for bodywork, such as, for example, automobile hoods and doors, tail gates and roofs, and can advantageously be carried out in only a single tool.
After cutting the starting blanks to shape they are placed in a special internal hydroforming (IHF) tool, to be described later, held sealingly together in their border regions, and then shaped :into a hollow body by means of the internal hydroforming (IHF) process. For stabilisation and final connection of the blanks these are clinched at suitable places. These manufacturing steps-holding sealingly, forming and clinching-can, according to the invention, be carried out with considerable advantage in only a single tool and in almost any desired order, as well as in combination.
The terms xe2x80x9chold sealingly togetherxe2x80x9d or xe2x80x9cholding sealinglyxe2x80x9d herein are to be understood as meaning a sealing together of the two blanks which makes it possible to apply the IHF process at least without any significant amount of pressure medium being able to escape to the exterior as the cavity or cavities between them is or are created. This can be achieved, for example, by the application of adhesive strips between the blanks, by edge forming of the flange regions of the blanks, or by a combination of the two. During the forming the flange regions or the sealing line or lines can also be subjected by suitable means, through suitable shaping of the tool, to a pressure sufficient for sealing. The pressure tightness is thus obtained by form-fitting. If the sealing pressure (pressing force applied along the sealing line) is adequate the blanks are, in addition, cold welded, at least in some places: while this is not essential for the method in accordance with the invention, it is nevertheless advantageous.
In an embodiment of the invention the blanks are plastically worked by pressing, preferably in the edge fold corner region: this leads to reliable sealing. For this purpose the tool-as described in more detail below-is modified by providing an additional draw ring as part of the lower draw punch.
In another embodiment of the invention at least one further processing step is performed in the special IHF tool during, in combination with and/or after the IHF process. These processing steps include, for example, stamping, punching and sealing, as well as at least preparations for the fitting of fasteners and the like.
For completeness it should be mentioned at this point that components from other branches of industry, such as, for example, flat radiators or similar articles, can also be fabricated using the method of the invention.